Known flexible couplings of this kind are often used to connect an engine flywheel to a driven component of the engine for example the gearbox or alternator. These couplings are substantially disc shaped having an inner metallic member connected to an outer metallic ring via a rubber body which is vulcanized to the inner member. The inner member of the coupling is connected to the driven component and the ring is bolted to the engine flywheel. The rubber body provides the torsional flexibility of the coupling.
In one particular known coupling the outer ring has a plurality of equiangularly spaced holes by means of which it is bolted to the flywheel. When the bolts are tightened, the face of the flywheel engages the ring. Resistance against backlash in this coupling is provided by the friction force between the flywheel face and the outer ring. This coupling is of limited flexibility because the rubber body is confined to the space between the inner member and the outer ring. Furthermore, blind assembly in this type of assembly, the flywheel carrying the ring and the driven component with the inner member are brought into engagement by feel without fitting or tightening any fixing elements which may be difficult to access as a result of housing structures in the engine, is not possible with this design as the bolts connecting the coupling to the flywheel need to be tightened.
In another known form of flexible coupling the rubber body has peripheral teeth which engage with corresponding teeth on the outer ring. The teeth on the outer ring and the rubber body allow the coupling to be assembled blind. This type of coupling has several disadvantages. Under load there is a tendency for adjacent engaging teeth to disengage, slip over each other and to re-engage with the next tooth. This causes undesirable wear on the teeth and ultimately can ruin the coupling. In transmitting torque the rubber teeth become compressed causing gaps to appear between the two sets of teeth. When the torque reverses, the presence of the gap causes backlash in the coupling. Furthermore, as a result of centrifugal forces generated during rotation of the coupling, the rubber teeth on the rubber body tend to swell during rotation and grip tightly the outer ring. This induces friction between them and effectively prevents axial movement between the rubber and the outer ring. Axial movement is desirable in flexible couplings to help provide compensation for any misalignment of the coupled components.